1. Field of the Invention
This invention relates generally to wireless local area networks; and more particularly to a protocol for peer-to-peer communications of wireless terminals.
2. Background of the Invention
Communication technologies that link electronic devices in a networked fashion are well known. Examples of communication networks include wired packet data networks, wireless packet data networks, wired telephone networks, wireless telephone networks, and satellite communication networks, among other networks. These communication networks typically include a network infrastructure that services a plurality of client devices. Wired Local Area Networks (LANs), e.g., Ethernets, are quite common and support communications between networked computers and other devices within a serviced area. LANs also often link serviced devices to Wide Area Networks (WANs) and the Internet. Each of these networks is generally considered a “wired” network, and the devices on those networks have essentially unlimited power supplies since they are connected to a wired power source.
Wireless networks have been in existence for a relatively shorter period. Cellular telephone networks, wireless LANs (WLANs), and satellite communication networks, among others, are examples of wireless networks. Relatively common forms of WLANs are IEEE 802.11(a) networks, IEEE 802.11(b) networks, and IEEE 802.11(g) networks, referred to jointly as “IEEE 802.11 networks.” IEEE 802.11 networks may operate either in Infrastructure Mode or in Ad Hoc mode. In Infrastructure Mode, a single node, termed an Access Point (AP), coordinates the actions of the other nodes and typically provides a connection to a wired network. In Ad Hoc mode, where an AP is not present, the wireless nodes jointly coordinate the WLAN. In IEEE 802.11 networks, the nodes may coordinate in one of two possible methods: the Distributed Control Function (DCF) or the Point Control Function (PCF). It is generally assumed that a Point Coordinator (PC) that provides the PCF is an AP within an IEEE 802.11 network operating in Infrastructure Mode.
WLANs provide significant advantages when servicing portable devices such as portable computers, portable data terminals, portable game terminals and other devices that are neither typically stationary nor tethered to power. Because these devices are battery powered, it is advantageous for these devices to turn off their radios and processing blocks as often as possible to conserve power. When an AP services the WLAN, the AP is usually tethered to a LAN connection and is connected to a wired power source. The AP therefore can continuously provide the PCF without interruption. However, in an Ad Hoc network, each of the WLAN devices is a peer such that none of the devices serves as an AP. Ad Hoc networks may require transmission coordination similar to that provided by the IEEE 802.11 PCF since all of the devices are peers. In a traditional system, the transmitter and receiver of the PC typically remain constantly powered via a wired source. In an Ad Hoc network, all devices may be battery powered so that none of the devices may reasonably service the PCF.
In the current IEEE 802.11 specification when operating in the PCF mode, devices (CF-pollable STA) may only transmit data when they have received a poll from the PC. After the device has transmitted its data, it expects to receive an acknowledgement message. If the data frame is not in turn acknowledged, the CF-Pollable STA shall not retransmit the frame unless the PC polls it again, or it decides to retransmit during the Contention Period (CP). (Section 9.3 of IEEE 802.11 specification). Thus the specified PC may receive transmissions when it is not powered and/or the PC may unnecessarily remain powered awaiting potential retransmissions.
Thus, there is a need in the art for improvements in protocols for WLAN peer devices that not only coordinate transmissions of peers that results in reduced power consumption, but that supports robust data throughput.